More of my thoughts:
1. Regarding interest in large events - this is hard to say myself because I'm one person but I would be. A lot of the organization is what actually encrouaged me to stick with the effort of going into deep space. The CG and knowing it was coming helped a ton, so FDEV buying into this I think will be the "make or break" for whether DW3 is high key or low key.
2. How it would work is also going to depend on FDEV buy-in, and what other mechanics/changes happen in the meantime. Bare minimum, reinforcing the DSSA is something I think is a very worthwhile and achievable goal even as a lower key event. I'd no doubt want more, but it's a minimal starting goal and one we as players can do without heavy buy-in. For what I'd love to see - maybe a narrative where an organization has commissioned commanders to find and establish sites for a sort of "backup bubble" if the Thargoids return in force again.
3. Ah carriers, the jump capable elephants in the room. Having a few official carriers is a good way to help people with limited time or resources participate and have a support structure for expeds, but yes, having everyone bringing theirs is going to get messy fast. I'd also not be surprised if "hostile" groups brought carriers for contrary purposes or to just be in the way. On our own, even if we took the hardest line and banned anyone who brought an unofficial carrier, nothing would stop them from still being there, so this again is an area where we'll need to depend on FDEV stepping up and playing ball in some fashion to limit how many carriers can go near or around a POI.